Take the mask-offset into account when rendering repeated image masks (bug 1799927)
Take the mask-offset into account when rendering repeated image masks (bug 1799927)

*Please note:* As usual when I'm working with the `src/display/canvas.js` code I don't really know what I'm doing, but it at least *appears* to work.

Snuffleupagus/pdf.js,Snuffleupagus/pdf.js,Snuffleupagus/pdf.js,Shoobx/pdf.js,showpad/mozilla-pdf.js,mozilla/pdf.js,showpad/mozilla-pdf.js,mozilla/pdf.js,mozilla/pdf.js,showpad/mozilla-pdf.js,Shoobx/pdf.js,Shoobx/pdf.js